Centralized traffic controlling system for railroads



Aug, 9, 1938. N. D. PRESTON 2,126,211

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Aug. 24, 1935 5 Sheets-Sheet l I F IG. 1.

ConTrol Of'fice Mvamm Aug. 9, 1938. N. 0. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS E iled Au 24, 1955 5 Sheets-Sheet 2 wZVEEZR 2 Aug 9, 1938, N. D. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Aug. 24, 1955 5 Sheets-Sheet 3 m f\n-1 5 Sheets-Sheet 5 N. D. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Flled Aug 24, 1935 Aug. 9, 1938.

Patented Aug. 9, 1938 PATENT OFFICE CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Neil D. Preston, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

. Application August 24, 1935, Serial No. 37,743

9 Claims. (01. 1 77-353) This invention relates to centralized traffic controlling systems for railroads and it more particularly pertains to the communication part of such systems.

In railroad traffic controlling systems the traffic is controlled from a control office usually located at a central point with respect to outlying field stations, thefield stations being connected to the control office by means of the communication system. The location of trains and'the condition of the traffic controlling devices at remote locations (outlying field stations) are indicated to the attendant at the control office by means of indications transmitted to the control ofice over the communication system. This invention is particularly useful in a system which is called upon to carry out a large number of controls and indications during a short time. A single dispatcher can handle the traffic over Q a large section of track so that it is desirable that the code combinations be capable of transmission at such a high rate of speed that the accumulation of stored controls and indications is avoided.

The switches and signals distributed throughout the territory and those located relatively near oradjacent each other, together with the apparatus provided to govern these switches and signals, are conveniently referred to as comprising a field station. The communication system is provided to interconnect the control ofiice with the several field stations and it is so organized that complete control and supervision of the various switch and signal devices at the remote stations are obtained by the operator. 7 Such a trafunsafe train movements, improper operation of track switches or the like.

In accordance with the present invention the communication system comprises three line wires extending from the control office through the several field stations in series. These three line wires are referred to in this disclosure as the S line, which is the stepping line and the A and B lines which are the return "line conductors. The S line, in addition to being used for controlling the stepping operations, is used for the transmission of controls by means of' polar impulses from the control o-fiice to the field stations. The S line also is used in combination with the A and B lines for the transmission of indications from the field stations to the control office.

All three line conduct r are normally deenerfic controlling system is supplemented by the usual automatic block signal system and other local means ordinarily provided to guard againstgized and the S line conductor is permanently connected to the B- line conductor at the last station of the series in order to form a closed circuit path for starting the impulsing operations over the S line from the control oftlce. The A line conductor is normally disconnected from the S and B line conductors at the last station of the series, but is arranged to be connected to the B line conductor at any station,'having new indications to transmit, for the purpose of initiating the system from the field station.

The line circuits are so arranged that any field stationin the series may so'control the line circuits .that the current in the A line, the B line, or both the A and B lines builds up at different rates of time, these rates being provided by the transmitting field station inserting or removing inductances from the A line, or the B line or both the A and B lines.

It is fundamental that the inclusion of an inductance in an electric circuit prevents current from rising in this circuit to its maximum value instantly, that is, a certain lapse of time is re-- quired before Ohms law; I=E/R. holds unless the effects of self-induction be eliminated or neutralized. The time constant is numerically equal to L/R- and is the time required for the current to rise to approximately 63% of its Ohms law value. For example, when potential is applied to a circuit containing one Ohm resistance and one henry inductance it takes approximately one second for the current to build up to the above value.

Advantage is taken of the above mentioned phenomenon to provide for the selective transmission of indications from a field station to the control ofiice in a centralized traffic controlling system. The detailed method of transmitting indications by the fast or slow building up of current in the A andB return line conductors of the system will be explained later in th specification.

Since the system is of the coded duplex type, it is operated through cycles, during each of which transmission of controls and/or the transmission of indications may occur. When controls are transmitted, a station selective code is first applied to the line for selecting the particular station with which communication is desired andthen the controls are transmitted to that station. Similarly when indications are transmitted, the particular field station transmitting such indications first transmits a station registering code for registering this station in the control office and then the indications are ticular controls to be transmitted to the selected station.

For the transmission of indications means are provided for energizing the S line during each impulse period by way of lines A and B and causing current to build up slowly or quickly in the A line alone, in the B line alone, or in both the A and B lines, for creating four code characters, any one of which may be selected at each step of the system for the transmission of indications. During the energizing'period of the S line circuit, with the return path established as above mentioned, it is deenergized at the end of each impulse period for causing the stepping apparatus in the office and at the field stations to take their steps.

For convenience in describing the operation in this system the energized or impulse periodsof the S line circuit will be referred to as the on periods, and the deenergized or time spaces between impulses of the S line circuit will be referred to as the off periods.

A system arranged in this manner materiall increases the capacity for'the transmission of indications over the capacity of the system for the transmission of controls. This is desirable in a centralized traific controlling system. since it has been found in practice that the number of indications desired for supplying the" proper information to the operator is greater than the number of controls necessary.

In the present embodiment all line conductors are normally deenergized. At the start of a control cycle of operations the S line circuit is energized with a impulse for conditioning the various relays of the system in order that the system may be properly responsive to the following impulses of the cycle. This first energization of the S line circuit is slightly longer than the other energized periods and is conveniently referred to as the conditioning on period.

At the start of a cycle of operations for the transmission of indications, the S line circuit is energized during the conditioning on perod of the system with a impulse-after which the stepping operations take place at the control oflice and the transmitting field station in synchronism.

The conditioning period is followed'by a num-- specification and claims and iurtherdetails will be better understood by referring to the accompanying drawings which illustrate one method and one modification for carrying out the invention by way of example.

The drawings illustrate in a diagrammatic manner the apparatus and circuits employed;

and for convenience in describing the invention in detail, those parts having similar features and functions are designated in the different figures by like reference characters, generally made distinctive either by the use of distinctive exponents representative of their location or by the use of suitable preceding numerals representative of the order of their operation and in which- Fig. 1 illustrates the line circuit arrangement for the control office and two field stations of a system embodying the present invention, including only the apparatus most closely associated with the line circuits.

Figs. 2A and 2B illustrate the apparatus and circuit arrangement employed at the control office for providing means whereby an operator may govern the switches and signals throughout an extensive territory and whereby indications may be received from the various field stations throughout such territory.

Fig. 3 illustrates the apparatus and circuit arrangements employed at atypical field station for providing control of a single track switch and for transmitting indications to the control ofiice in accordance with the present invention.

Fig. 4 illustrates a modification of the indication receiving circuits in the control ofiice; and

Fig. 5 shows in detail the control circuits and apparatus for controlling relays CD and [LC shown in Fig. 2A.

When tracing the circuits, Fig. 2B should be placed below Fig. 2A and Fig. 3 should be placed to the right of Fig. 2A, with correspondingly numbered lines in alinement.

For the purpose of simplifying the illustration and facilitating in the explanation, various parts and circuits have been diagrammatically shown and certain conventional illustrations have been employed. The drawings have been made more with the purpose of making it easy to understand the operation of the invention than with the idea of illustrating the specific construction and arrangement that would preferably be employed in practice.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of current and the circuits with which these symbols are used always have current flowing in the same direction. The symbols (3+) and (B) are employed to indicate the positive and negative terminals respectively of a suitable battery or other source of current having an intermediate tap (CN) and the circuits with which these symbols are used may have current flowing in one direction or the other depending upon whether the terminal (B+) or (B-) is used in combination With tap (CN).

General description The three wire line circuit which connects the control ofiice with the field stations is indicated in schematic form in. Fig. 1, This figure shows that all three line conductors are normally deenergized.

It is to be understood that the system may be extended to include as many field stations as desired; but for convenience in describing the present invention only a first anda last field station have been illustrated. The S line is connected in series with the line relays at all field stations including the last'station where this line is permanently tied to the B line. The S line includes a neutral line relay F in the control office and a three position biased-to-neutral polarized line relay F (with suitable exponent) at each field st'ation.: In the control ofiice the A line is connected to the terminal of line battery LB by Way of back contact I5 of starting relay S'I'Ryand the B line is connected to the terminal of bat tery LB by way of back contact i l of relay STR. This applies a potential to the A and B line conductors so that these conductors may be energ ized by connecting them together at an initiating field station.

By referring to Fig. 1 it will be noted that inductance units AL and AL are included in the A line circuit by the picking up of relays PLA or PLA respectively, with these inductance units being short-circuited when the associated relays are not picked up. Inductance units BL and BL are likewise inserted in or removed from the B lineconductor by the picked up or dropped away condition of the associated PLB relays. As above mentioned, indications are transmitted by iiicluding these inductance units in or excluding them from the associated return line conductors.

The A and B line conductors are connected in series with message relays MA and MB in the control office; and during the transmission of indications, the sequential order in which these message relays are picked up determines the particular indication which is to be received, itbeing understood that this sequential order is determined at the transmitting field station by including the inductance in the associated line or excluding it from this line.

Control office equipment-The control oflice (see Figs. 2A and 213) includes a control machine having a group of control levers for each field station, a miniature track layout corresponding to the track layout in the field and various indicatinglamps or equivalent devices, together with apparatus and circuits to accomplish the desired operation of the system.

That part of the control ofiice illustrated shows more particularly the portion of the control machine which is typical of the apparatus associated with a single field station having a track switch, a cross-over or the like, together with the general transmitting apparatus employed for all field stations.

This apparatus for one track switch comprises a switch machine control lever SML, a self-restoring starting button S'I'B, a miniature track switch its and a track occupancy indicating lamp OS. Similarly one or more signal control levers are also provided, but for convenience these levers have been omitted since the control of a track switch by lever SML is typical of the control of other types of trafiic controlling devices.

The movement of lever SML from one extreme position to the other, followed by the actuation of button STB results in the normal or reverse operation of the track switch corresponding to this lever located at the field station corresponding to this button. The momentary actuation of button STB is stored by a storing relay SR (see Fig. 5) which in turn picks up the associated code determining relay CD for the associated station. It will be understood that there is a storing relay and a code determining relay for each starting button representing a field station. These relays are so interlocked that irrespective of the number of storing relays simultaneously picked up in response to the simultaneous or rapid actuation of corresponding starting buttons, only one code determining relays will be successively energized during successive cycles in a predetermined order in accordance with their relative location in the code determining bank of relays.

An indication change relay ICH (see Fig. 5) and an indication code relay iLC are associated with the bank of storing relays SR and code determining relays CD for the purpose of providing initiation of the communication system when a change in condition takes place at any field station or in the control office of the system. This indication change relay ICH and indication code relay iCL, together with the storing relays SR and the code determining relays CD are associated with a code stick relay LCS and are so interlocked with this relay LCS that the picking up of a CD relay or the ILC relay is prevented during an operating cycle. The circuits of this interlocking bank of storing and code determining relays are shown conventionally by dottedlines in Fig. 2A and shown in detail in Fig. 5 in the present disclosure.

. The same means of providing this interlocking arrangement of the code determining and code indication relays is also disclosed in applicants prior application Ser. No. 711,383, filed February 15, 1934, and in the corresponding Canadian Patent No. 364,307, dated February 2, 1937. For the purpose of understanding the present invention it is only necessary to understand that relay CD is picked up during a cycle for the transmission of controls to the associated field station, as well as being picked up during a duplex cycle when controls are transmitted to the associated station and indications are transmitted from this station or some other station during the same cycle. The relay CD is for instance picked up by relay SR, and relay SR (see Fig. 5) is picked up by the depression of push button STB, resulting in the closure of a pick-up circuit including this push button contact. Relay SR will then be stuck up through a stick circuit including back contact 2! of the particular relay CD directly associated with this relay SR. With a particular relay SR energized, and upon restoration of the system to its normal inactive condition, a pick-up circuit for the relay CD including the back contact iii of relay SA, the back contact ll of relay LCS and the front contact 13 of the relay SR is closed. With the relay CD energized and its front contact 26 closed the starting relay STR is energized thereby starting the system into operation. It may be pointed out that the relay SR which was originally stuck up through a stick circuit including the back contact 2i of the relay CD is now stuck up by a stick circuit including the front contact 2! of relay CD and the back contact 75 of the relay LCS. Initiation of the system into a cycle of operation. causes the relay SA to assume its energized position thereby closing a stick circuit for the relay CD including the stick contact "M of this relay CD and also including the Winding of a series relay LCS. The relays CD and LCS are therefore stuck up in series in a stick circuit which is maintained throughout the cycle of operation of the system. The picking up of the relay LCS as, just explained therefore results in the opening of the stick circuit for relay SR and in the deenergization of the relay SR.

As pointed out hereinafter the system is initiated into operation by any one of the field stations by the picking up of a relay PLA (see Fig. 1) having an exponent corresponding to that station. The picking up. of such relay PLA connects the A line and the B line together at that station through the upper winding of a lock-out relay LO. Since the battery LB is normally connected across the line wires A and B the closure of the circuit portion through the upper winding of the lockout relay LO results in the picking up of this relay L in series with the relays MA and MB in the control oflice (see Figs. 1, 2A and 5). Referring now to Fig. 5 it will be noted that the picking up of the relays MA and MB closes their respective contacts BI and 60, thereby closing a pick-up circuit for the indication change relay ICH including these contacts 60 and 6! and including back contact 10 of the relay SA, this of course being on the assumption that the system is then at rest and the relay SA is in its deenergized condition. With the indication change relay ICH energized a stick circuit including the stick contact 16 of this relay and including the back contact of the relay LCS is closed.

With the indication change relay lCI-I energized by its stick circuit, and assuming that all of the relays SR are in their deenergized condition, a pick-up circuit for the indication code relay ILC including contacts 10, H, T3 and I1 is closed. With this relay ILC once picked up it is stuck up through a stick circuit including its stick contact 18, the winding of the relay LCS and the front contact 1B of the relay SA included in series. The relay ICI-I is of course deenergized when its stick circuit is broken by the opening of contact 15 of relay LCS. The relay ILC isof course deenergized at the end of the indication cycle upon restoration of the relay SA to its normal deenergized condition. When a particular relay CD is energized the front contacts 36, 48, 52 and 53 connect certain control levers to the system to cause the application of a polarity code to the line circuits to control particular apparatus in the field in accordance with the positions assumed by these control levers. If, on the other hand, the indication code relay ILC is energized its contacts 34, 42, 43 and 44 result in the application of a phantom code to the stepping circuit which code has a polarity characteristic such as not to select any field station, but to cause operation of the stepping relays to enable a particular field station to send an indication code to the control office.

The control ofiice includes, in addition to the line relay F above mentioned, a neutral quick acting line repeating relay FP and a neutral slow acting line repeating relay SA. Relay FP repeats each energization of relay F and relay SA is picked up at the beginning of each cycle, remains up throughout the cycle and is dropped at the end of the cycle. Relay SA has such characteristics that its pick up time is relatively long compared to the pick up time of neutral relays such as relay FP, but its pick up time is relatively short as compared with its drop away time. The drop away time of relay SA is of suflicient duration to maintain its contacts in their picked up positions between successive impulses applied to the S line circuit as repeated by relay FP.

Associated with the line repeating relays is a bank of stepping relays including relays IV, 2V

and 3V together with the half-step relay VP.

This bank of stepping relays is for the purpose of marking off the successive steps of each cycle. An impulse controlling relay E is jointly controlled by the stepping relays and the half-step relay and is for the purpose of energizing and deenergizing the S line circuit for providing the on and oft periods of the cycle.

Code sending relays PC and NC are for the purpose of providing the proper polarity of energization of the S line circuit during the transmission of the control impulses. With relay PC energized and relay NC deenergized, potential is applied to line S from battery LB; and when relay NC is energized with relay PC deenergized, potential is applied to the S line circuit. For convenience in the description it will be assumed that potential applied to line S positions the contacts of the polar line relays at the field stations to the right, and potential applied to line S positions these contacts to the left.

Starting relay STR is for the purpose of initiating the system into a cycle of operations in response to a control start, when relay CD picks up, or for an indication start when relay ILC picks up. Since relay CD is picked up during a duplex cycle, relay STR is operated to start the system irrespective of the type of cycle which follows.

Message receiving relays MA and MB are provided to receive the messages from a transmitting field station and these relays in turn control message receiving repeating relays MAP and MBP for registering or storing the received indications for a period of time suflicient to operate the selected indication receiving relay.

A timing check relay TC is provided for measuring off a predetermined period of time, this time being fixed by the adjustment of timing inductance unit TL to cause relay TC to pick up when energized in approximately the same timethat relay F in the S line circuit picks up when no limiting inductance is in either the A or the B line conductors. The purpose of this timing check relay will be explained more in detail later.

For the purpose of illustrating station registration, two pilot relays [PT and 2PT are shown in Fig. 2B, these relays being controlled on the first ,1

step. It will be understood that similar additional pilot relays may be provided for the second step and so on until a suflicient number of codes for station registration have been provided as required by the size of the system. These pilot relays are of the two position polar magnetic stick type, although it is to be understood that any suitable arrangement of pilot relays may be employed for selecting station relay ST. Indication receiving relays IIR. and HR are provided for storing the indications as received by the MAP and MBP relays at the various steps of the cycle. These two indication receiving relays are shown as being selected on the second step of the cycle and it will be understood that additional similar relays may be provided for additional steps to accommodate the total number of indications to be received during the cycle.

Indication lamps, such as the track occupancy lamp OS, are provided to illustrate the manner in which indication conditions at a particular field station are displayed in accordance with the present invention.

Field station equipment-The field station illustrated in Fig. 3 is typical of all stations of the system and may be adapted for use at the first, second, or any other location by merely altering certain code jumpers to arrange for the desired codes. For convenience in the description this field station has been specifically illustrated as being the first station of the series by reason of the distinctive exponents employed.

A turnout track is illustrated as connected to a main track by means of a track switch TS This track switch is operated from one extreme locked position to the otherby means of switch machine SM Switch machine SM is operated by a switch machine control relaySlVfRl of the two lposition polar magnetic stick type governed from the. control office through the medium of the communication system herein disclosed. Relay SMR con trols the operation of'the switch machine by energizing its normal or reverse operating wires from a local source of current, it being assumed that the switch machine is operated to its normal locked position when the polar contacts of relay SMR are actuated to'the right; and when these contacts are actuated to the left, the switch machine is operated to its reverse locked position. It will be understood that this control preferably includes suitable approach locking means and such other automatic signalling circuits as are usually employed but which are not shown in the present disclosure for the sake of simplicity.

Suitable signals are associated with track switch TS for governingtrafiic thereover and are provided with automatic signalling'means interrelatin'g this trafiic overthe track switch with a control relays operated from the control oiiice in a similar manner disclosed in connection with switch machine control relaySMRJ; all of which has been omitted from the present disclosure in order to simplify the drawings and description.

A detector track section having a normally closed track circuit with the usual track relay T and a suitable track battery are also associated with the track switch for indicating the passing of trains. It will be understood that suitable indicating means are provided in con nection with the track switch and the switch machine for indicating the locked or unlockedconditionof this apparatus, this portion of; the system likewise being omitted from the present disclosure. 9i e Forthe purpose of indicating how indications are transmitted by conditioning the A line at each step of the system, track relay T is shown with itscontact picked up and an explanation will be given of the-marinerin which the picked up or dropped away condition of the track relay is transmitted to the contr'ol oifice by' the fast or slowbuilding up of current in the A line con ductor. For indicating how indications are transmitted over the Blihe conductor at the same step, signal repeating relay M is shown with its contact in its dropped away-position. It will be explained how the position-bf this-re lay is transmitted to the control ofiice bythe quick or slowbuilding up of current invtheB line conductor at the same step that indications are transmitted over the A line conductor.

The communication part of thesystem includes the previously mentionedline relay F and its quick acting repeating relay-FP Slow acting relay SA is for a purpose similar to that explained in connection with relay SA in the con- Relays FE and SA have characteristics similar to the corresponding relays in the control oifice; but in order to prevent unnecessary stepping operations at stations not selected, the circuit arrangement of these relays is different from the corresponding control relays as will be later pointed out. i 1 a The .field station includes a bank of stepping relays 1V 2V 1and 3V with the associated halfstep relay .VP arranged to operate in synchronism with the corresponding relays in the control ofiice. l The detailed circuits for the stepping and h'alfj-step relays in the control office and at the field station have not been shown, it being considered .sufiicient to merely point out in the following description when these-lrelaysare energized and deenergized during the 01f and on periods of a cycle. The detailed circuits for operating thesestepping relay banks may be the sameas .disclosed in applicants prior application Ser. No. 711,383.

For the purpose of illustrating the selection of a. station. for the transmission of controls, relay SO has been shown; but it will be understood that any suitable station, selecting arrangement maybe employed without departing from the spirit of the present invention. Afield change relay CH is provided to register a change in any of the traffic controlling devices at the'station so that the system will be initiated for thetransmission of new indications. The detailed circuit for controlling this relay has not been shown since it isimmaterial to an understanding of the present invention. It need only be mentioned that relay CH normally energized, is dropped in response toajchange in condition of a device at the station which requires the transmission of indications during a succeeding cycle and this change relay is resensitized or picked up during this cycle in readiness for its response to a succeeding change in a traffic device.

For the purpose of illustrating the manner of determining when this field station is to transmit its new indications, lockout relay L is employed. When relay L0 is picked up during a cycle of operations to permit the field station to transmit, the A line indication transmitting relay PLA and the B line indication transmitting relay PLB are governed in accordance with the code jumpers and the indication contacts for this station, so that the A and B line conductors are distinctively conditioned for registering this station in the control office and for transmitting the various indications- Inductanceunits AL and BL are included in and excluded from the A and B line conductors respectivelyby the operation ofthe PLA and PLB relays.- By referring to the dotted rectane gle in the upper right hand portion of Fig. 3 it will be seen that similar inductance units are controlled by similar PLA and PLB relays atthe other stations associated with the system.

. i A resistance B is employed to compensate for the difierent locations of thefield stations during the functioning of the lookout .feature of the system. In other words, the field station at the end of the line needs no such resistance; but at each station nearer the control ofiice a higher resistanceis provided so that approximatelythe same current from line battery LB in the control ofiice flows through the lower winding of lockout relayirrespective of the particular station which is transmitting. v H

It is believed thatthe nature of the invention, its advantages and characteristic features will best be understood with further description being set forth from the standpoint of operation.

' Operation The'system of the present invention is normally in a condition of rest from whichit may be initiated into acycle of operations either from the control office or from-any one of thefield stations when there are new bontrols or new indications respectively ready to be transmitted. If new controls for severaldifferent field stations are ready for transmission at substantially the same time, they are transmitted on separate cycles, one station for each cycle. Similarly, if several field stations have indications ready for transmission at the same time, they are transmitted from such field stations to the control office, one station for each cycle.

It may happen that there are new controls and new indications ready to be transmitted at the same time, and in such instances controls are transmitted to a selected field station simultaneously with the transmission of indications from the same or some other field station during the same cycle.

Irrespective of whether a cycle is to be for the transmission of controls and/or the transmission of indications, a predetermined number of impulses are placed upon the S line circuit to accomplish the step-by-step operation of the stepping relay banks. These impulses are time spaced, that is, they follow each other at definite time intervals. Conditioning takes place during the period of time that the S line circuit is deenergized between impulses (off periods). In other words, during the off periods, the desired control and message relays are selected; and during the succeeding on periods, the selected circuits are energized in accordance with the particular code combination applied to the line during these on periods.

When a cycle is initiated for the transmission of controls, the character of the impulses placed upon the S line circuit is determined in accordance with the station to be selected and the controls to be transmitted, as set up by the code jumpers and the control levers for that particular station. During a cycle of operation initiated for the transmission of indications alone, the character of the impulses placed upon the S line circuit is such that no station will be selected, but these impulses merely cause the step-by-step operation of the control ofiice stepping relay bank and the particular field station which is transmitting. A series of impulses which selects no station for an outbound call is referred to as a phantom code.

When a cycle of operations is initiated from a field station for the transmission of indications, the plurality of impulses placed upon the S line in the control office to cause the step-by-step operation are returned to the control ofiice by way of one or the other of the A or B line conductors or the A and B line conductors in multiple, with the rate at which current is allowed to build up in the A and B line conductors determining the indications which are to be transmitted.

Normal at rest c'onditions.-Although the system may be initiated from the field stations, the three wire line circuits are normally deenergized. In order to provide a means for initiating the system from a field station, the normally deenergized A-B line circuit is energized m a manner which will be later pointed out. The remaining circuits of the system are likewise normally deenergized, with a few exceptions.

For example, the track circuit associated with track switch TS is preferably of the closed circuit type so that relayT is normally picked up. Also, the field change relay OH is normally energized over a circuit not shown.

M anualstartWith'the system in a condition of rest, itmay be manually initiated into a cycle for the transmission of controls. Whenever such a cycle desired the operator first positions the control levers for the field station which he desires'to select-and then actuates the starting button STB associated with the station.

For the purpose of considering the operation of the present systemit will be assumed that lever SML=of Fig. 2A is positioned to the right for operating the track switch of Fig. 3 to its normal locked position and that the starting button STB is actuated to start the cycle of operations. The actuation of button STB causes relay CD to be picked up and stuck up until the end of the cycle which is initiated by the picking up of relay CD.

A circuit is now closed for picking up relay STR which extends from front contact 26 of relay CD and winding of relay STR. to A circuit is now closed for picking up relay PC which extends from back contacts 39, 38 and 31 of relays 3V, 2V and IV respectively, front contact 36 ofrelay CD, winding of relay PC and front contact 33 of relay STR, to

The picking up of relay PC applies the first conditioning impulse to the S line circuit (which in this event is positive) over a circuit which may be traced from the terminal of battery LB, front contact I2 of relay PC, back contact l3 of relay NC, winding of relay F, back contact 32 of relay E, S line conductor l8, winding of relay F through the line relays at other stations, winding of relay F at the last station, back contact 304 of relay PLB at the last station, back contact 204 of relay PLB at the first station, B line conductor l9, winding of relay MB, front contacts l4 and I5 of relay STR, back contact I6 of relay NC and front contact 25 of relay PC to the terminal of battery LB. It will be noted that the A line conductor is not energized at this time because of the open front contact on the SA relay at the last station, which relay is not yet picked up.

In response to this energization of the S line circuit, relay F in the control offlce is picked up and the line relays at the field stations, including relay F actuate their polar contacts to the right.

The picking up of relay F closes a circuit at its front contact 40 for energizing relay FP. Contact 200 of relay F in its right hand position closes a circuit for picking up relay FP which circuit extends through back contact 20I of relay SA At the same time this circuit extends through back contacts 202 and 201 of relays L and S0 respectively and winding of relay SA to for energizing relay SA It will be understood'that the line repeating relays, including the slow acting relays, at the other stations along the line are picked up substantially in synchronism with corresponding relays at the first station illustrated in Fig. 3. When relaySA at the end field station closes its front contact 306 (illustrated in the dotted rectangle in the upper right hand portion of Fig. 3), the A line conductor is connected in multiple with the B line conductor so that current returns to the control'ofiice over these two conductors in parallel.

When the B line conductor was energized at the beginning of this conditioning on period over the above described circuit, relay MB was picked up and when the A line conductor is energized a little later in the on period, relay MA is picked up. It will be noted that front contacts l4 and I of relay STR in the control ofiice connect the A and B line conductors in multiple at the control office end of the circuit.

The picking up of relay MB closes a circuit for iii) and (13-) contacts on the MAP relay connect.

are not yet selected, this. operation of relay MAP is of no effect. When relay E; is picked up to mark the end of this conditioning on period (as will be later described), the above described stick circuit for relay MAP is opened at back contact 55 and this relay is deenergized, before relay IV is picked up to make the selection of the first channel circuit.

During the conditioning on, period, relay SA- in the control oflice is energized over a circuit completed at front contact 4| of relay FP. During this period, relay SA at the station is energized over the above described circuit including contact 209 of relay F and also at front contact 298 of relay FP Polarity selection of stepping impuZses.When the system is initiated by the picking up of relay STR due to a manual start condition, the first impulse placed upon the S line circuit is positive in character by reason ofthe picking up of relay PC as previously described. This application of energy to the S line circuit causes various relay operations, a portion of which have been described, while that portion of the relay operations relating to the half-step relay and the stepping relays will be pointed out later.

It will be assumed for the present that after a predetermined time the S line circuit is deenergized by the picking up of relay E. This deenergization of line S results in the energization of the first steppingrelay IV. The picking up of relay IV opens back contact 31 included in the above described pick up circuit for relay PC and closes front contact 37, which will again energize relay PC during this off period over the previously described circuit from which now extends through front contact 31 of relay IV, front contact 48 of relay CD, code jumper ll in its full line position, winding of relay PC and front contact 33 of relay STR, to This picking up of relay PC determines that the character of the next impulse will be and the line circuit is energized in the same manner as described for the conditioning impulse.

In the event that code jumper 41 is connected in its dotted line position, then the circuit through front contact 48 of relay CD is effective to pick up relay NC which, by means of its contacts l3 and it being picked up and contacts 12 and 25 of relay PC being dropped, reverses the connection of battery LB to the line circuits so that line S is energized with a impulse. Such control of relays- PC and NC upon the picking up of relay IV occurs during the first off period,

that is, during the deenergized condition of the stepping line circuit following the initiating on period.

After the first impulse has beenconnected to the control line circuit for a predetermined period of time, the line is again deenergized by the picking up of relay E. Such deenergizaticn of the S line causes the second step to be taken by picking up relay 2V. Relay 2V closes a circuit for picking up relay NC which extends from (+),back contact 39 of relay 3V, front contact 38 of relay 2V, front contact 52 of relay CD, jumper 49 in its full line position, winding of relay NC and front contact 33 of relay STR, to It will be obvious that relay PC would be picked up on this step in the event. that code jumper 49 is connected in its dotted line position. The code which is selected for the third step in the present embodiment is determined by the position of lever SML. With this lever in its right hand position as. shown, relay PC is energized on the third step over a circuit extending from front contact 39 of relay 3V, front contact 53 of relay CD, contact of lever SML in its right hand position, winding of relay PC and front contact 33 of relay STR, to This p-redetermines that a impulse is applied to line S during the third on period. In the event that lever SML is in its left hand dotted position, then relay NC would be picked up to apply a impulse to line S during the third on period.

This operation occurs on each step so that relays PC and NC are selectively energized in accordance with the particular code which is to be transmitted for each step. During the first part of each operating cycle, these relays are energized during the station selecting steps of the stepping relay bank in accordance with the character of the code for the station desired to be selected. During the remaining steps of the cycle these two relays are selectively energized in accordance with the positions of the control levers associated with the selected station. It will be understood that additional levers for the control of signals or the like may be provided and selected through additional contacts on relay CD for selectively energizing the PC and NC relays during additional steps (not shown) of the cycle.

From the above it will be seen that the impulses applied to line S always begin with a impulse for a cycle initiated from the control ofllce, while the following impulses are or dependent upon the code jumpers and control levers rendered effective by the particular code determining relay which is picked up for that cycle. Also this polarity determination is accomplished by the two code sending relays PC and NC selectively energized at the several steps, with the changes in selection occurring while the S line is deenergized.

Impulsing and stepping operations-irrespective of the particular polarity with which stepping line S is energized, relay F in the office is picked up and the F relays at the various field stations, are actuated either to their right or left hand positions for picking up their associated FP relays. For example, the closure of contact 209 of relay F in either its right'or left hand position closes a circuit through back contact 2M of relay SA for picking up relay FP The field station stepping circuits in the present embodiment are so arranged that stepping is discontinued at field stations not selected. This is determined by relays L and S0 (of Fig. 3, for example), either one, the other or both of which will be picked up as long as this station remains in active communication with the line circuit. This feature will be more specifically pointed out later, but for the present it is to be noted that relay FP acts as a repeater of relay F as long as either front contact 202 of relay L0 or front contact 20'! of relay S0 is closed. Therefore it Will be assumed that relay FP of Fig. 3 repeats all of the impulses applied to the line circuit during this assumed cycle of operations. This is because relay S at this particular field station will be picked up throughout the cycle in a manner to be later described.

As above mentioned the detailed circuits for operating the step and half-step relays are not shown in this disclosure, it being considered sufficient to merely point out when these relays are energized and deenergized. At the beginning of the transmitting part of the cycle, marked off by the picking up of relay SA in the control office and similar relays at the field stations, the half-step relays including relay VP in the office of relay VP at the illustrated field station, are picked up for preparing the stepping relay circuits for the first step, which step is taken during the next off period. In brief, the half -step relays VP and VP are picked up and dropped alternately and in synchronism by the successive energizations of the stepping line circuit and the stepping relays are picked up in succession for each successive deenergization of the stepping line circuit. This means that the VP relays first pick up during the conditioning on period, then drop during the first on period, are again picked up' during the second on period and dropped during the third on period. Since three steps are assumed in the present embodiment, the VP relays remain deenergized after dropping during the third on period. Likewise, the IV relays pick up during the first off period (following the conditioning on period), the 2V relays pick up during the second off period and the 3V relays pick up during the third off period, with these relays being stuck up until the end of the cycle.

When relay VP is picked up during the conditioning on period, a circuit is closed for picking up relay E which extends from front contact 90 of relay MA, front contact 9| of relay MB, front contact 92 of relay VP, back contacts 93, 94 and 95 of relays IV, 2V and 3V respectively and winding of relay E, to Relay E closes a stick circuit for itself by way of its front contact 96, front contact 9'! of relay SA and over the remainder of the previously described circuit to the winding of relay E. It will thus be seen that the energization of relay E to mark the end of an on period is dependent upon the energization of both the A and B line conductors which causes relays MA and MB both to be picked up.

In response to the picking up of relay IV during the first off period, the above described pick up and stick circuits for relay E are opened at back contact 93 of relay IV which allows relay E to drop. It will be obvious that the opening of back contact 32 of relay E terminates the conditioning on period by deenergizing the S line circuit, and likewise the closure of this back contact when relay E drops terminates the first off period by energizing the S line circuit.

When relay VP is dropped in response to the first impulse, relay E is picked up over the above described pick up circuit which now includes back contact 92 of relay VP and front contact 93 of relay lV. Relay E again closes its previously described stick circuit.

When relay 2V picks up in response to the second off period, the above described circuit for relay E is interrupted at back contact 94 which allows this relay to drop and again energize the S line circuit which was deenergized when relay E relay 2V. Relay E deenergizes the S line circuit at back contact 32 and closes its above described stick circuit.

When relay 3V picks up in response to this third deenergization of the S line circuit, the circuit of relay E is opened at back contact 95, allowing relay E to drop and again energize the S line circuit.

When relay VP drops in response to the third impulse, relay E is energized over the above described circuit which now includes back contact 92 of relay VP and front contact 95 of relay 3V. Relay E opens back contact 32 for deenergizing the S line circuit and again closes its stick circuit.

Since there are no more stepping relays the above described stick circuit for relay E is maintained complete for a comparatively long interval of time which maintains the S line circuit deenergized for a suificient period of, time to drop the SA relays to mark the end of the cycle.

The dropping of relay SA deenergizes the stick circuits for the stepping relay bank which allows the stepping relays to be released. The opening of front contact 91 of relay SA deenergizes the stick circuit for relay E which allows this relay to be released. The opening of front contact 10 of relay SA (see Fig. opens the stick circuit for relay CD including winding of relay LCS in series. Similarly, the dropping of the SA relays at the field stations deenergizes the holding stick circuits for the stepping relays at the station at which these relays have been operating during this cycle. It will be understood that relay CD is deenergized by the dropping of relay SA and this relay in turn deenergizes relay STR and the circuits leading to the PC and NC relays are likewise opened by the dropping of relay CD.

It will be understood that relays MA and MB are picked up and dropped substantially in synchronism with relay F during a control cycle and since these relays are dropped at substantially the same time and picked up at substantially the same time, the circuits are not completed for energizing repeating relays MAP and MBP. The energization of these repeating relays will be explained in connection with an indication cycle.

With relays MAP and MBP deenergized at each step of the control cycle the executing circuits shown in Fig. 2B are effective to position pilot relays IPT and 2PT to the left because the energizing circuits for these pilot relays extends from (B) at back contacts of relays MAP and MBP. With the contacts of relays [PT and 2PT both positioned to the left no station relay is selected. In other Words, a combination of quick energization of the A and B line conductors during the station registration steps of the cycle corresponds to a phantom code and results in the selection of no station relay. After the station selection steps are taken, then with no station relay picked up the following steps are ineffective to energize any of the indication receiving relays because of the open front contacts on the station relays.

It is to be understood that these circuit connections may be extended for as many steps as desired, with alternate off periods picking up additional stepping relays and alternate on periods shifting the BP relays in a manner similar to that already described.

The stepping relay banks at all of the field stations are substantially identical with the one illustrated in Fig. 3. The operation of the field station stepping relay bank is effected by the intermittent operation of relay FP in a manner which is indicated by the connection through back contact 2090f relay FP front contact 209 of relay SA and the dotted line leading to the stepping relay bank. As above pointed out the lays L and S0 Therefore after relay 8A 0% "the stepping operationat these stations doesnot take place.

Station selection for controlszlhe application of a predetermined number of impulses of selected'polarities to the S linecircuit to comprise kja cycle of operations has been explained in detail. For the transmission of controls the first" impulse is alwayspositive in character, with thefollowing impulses positive or negative in accordance with the particular code jumpers and control levers Ouwhich are effective for the cycle. Referring to Figs. 1 and 3 it willbe obvious that these impulses are received at all of the field stations since the field station line relays are all included in the stepping line circuit. However, for convenience 5111111 describing the operation of station selectionreference will be made to Fig. 3 which illustrates a typical field'station somewhat in'detail and whichfor convenience-is considered the first sta. tion of the series.

5.: The first impulse in'the stepping line actu- -of front contact 208 of relay FP establishes a direct energizing circuit for relay SA and since it isassumed that the station illustrated in Fig. 3 is the station to be selectedduring this cycle; relay FP will intermittently close its front contact 286 ;;for maintaining relay 3A picked up throughout the cycle.. It is tobe understood that the first impulse (conditioning on impulse) is somewhat longer thantheremaining impulses of the cycle so that relay SA andother similar relays at other stations have time to pick up during the time that the stepping line circuitis energized.

Duringthe conditioning on period, relay S0 is energized over a circuit extending from back contact 21!! of relay SA back contacts 2|2,

Band 2 l l of relays 3V 2V and W respectively,

contact 2 of relay F in its right hand dotted position andwindingof relay S0 to Relay S0 connects by way of its front contact M5 to the above described. circuit independent 0f back contact 210 of relay SA which. maintains relay S0 energized after the picking up of relay. SAL It will be understood that similar circuits are established at all other field stations for picking up the associated SO relays and that the same operations take place at these other stations with exceptio-nsrlater to be explained.

It the conditioning impulse is for reasons to-be later explained, the polar contacts of relay F are positioned to the left which prevents the uenergization of relay S0 since the above described pick up circuit is open with contact 2H in itsleft hand dotted position, and since the pickup circuit of relay S0 isinterrupted after contact 2"] of relay SA is shifted from its back 5 to itstfront position Since the picking up of relay S0 registers the fact that a impulse was transmitted during the conditioning on period, the stepping relays at the station illustrated in Fig. 3 complete their operations, While at those stations not to be seelected, the stepping relayoperation is discontinued when the SO relays at those stations drop out to effect the opening of the FP relay circuits at front contacts similar to 261" of the various S0 relays.

At the station illustrated in Fig. 3; relay FP repeats the operations of relay F by means of a circuit which extends from contact 2'65] of relay F in either of its dotted line positions, back contact 202 of relay L0 front contact 267 of relay S0 and winding ofrelay FP to Relay VP is picked up during the conditioning on period over a circuit which is not shown.

As pointed out above the character of the first impulse (following the conditioning on period) is determined in accordance with the position of jumper 4! in the control offi'ce. With this jumper connected as shown in Fig. 2A, a impulse is applied to the stepping line circuit which positions relay F to the right and closes a selecting stick circuit for relay so which extends from front contact 215 of'relay SO back contacts 2|2 and 2| 3 of relays 3V and 2V respectively, front contact 2l4of relay IV co'de jumper 2H5 in its full line position, contact Zll of relay F in its rig-ht hand dotted position and winding of relay S0 to If 'code jumper is connected in its dotted line position, then a impulse is applied to the stepping line because this position of the first code jumper effects the energization of relay NC in stead of relay PC, which is effective to actuate the contacts of relay F to their left hand dotted positions. With contact 2 of relay F in its left hand dotted position, then the circuit leading through the contacts of the stepping relays to jumper H6 is not completedto the winding of relay S0 so that this relay is dropped in response to a code combination comprising a first impulse.

Similarly, with the first impulse at those stations with code jumpers similar to 2; arranged as shown by the dotted line connection of this code jumper, the circuits to the SO relays are incomplete so that they are dropped out. The opening of a contact similar to contact 201 of those stations which fail to be selected disconnects the circuit leading to the relays similar to FP so that stepping does not occur at such stations.

During the off period following the first on period, stepping relay 2V is picked up and the polar contacts of relay F are restored to their neutral positions. This deenergizes relay FP and since relay S0 remained picked up dur ing the first on period'a stick circuit is now completed for this relay which extends from front contact 2l5 of relay S0 front contact 2H] of relay SA back contact Eii'i of relay FF and winding of relay S0 to- Upon the application of the next impulse which follows the picking up ofrelays 2V and 2V relay tion, contact 2| I of relay F in its left hand dotted position and winding of relay S to From the above it will be apparent that relay S0 at the station to be selected is energized by means of its selecting circuit including code jumpers H6 and 222 and contact 2 of relay F in either a right or a left hand dotted position during the impulse or on periods of the station selecting portion of the cycle. Make-beforebreak contact 2!! of relay F establishes a stick circuit for relay SO during the off periods, which extends from front contact N5 of relay S0 front contact 2 IU of relay SA contact 2| I of relay F in its neutral position and winding of relay S0 to Contact 2 in its neutral position is in multiple with back contact 2H of relay FP so that the stick circuit for relay S0 is established immediately upon the opening of the selecting circuit by contact 2H and before relay FP is deenergized to close its back contact 2".

In brief there are a plurality of code determining means in the control oflice each including a code determining relay and a set of code jumpers, only one of which relays may be effective to determine the character of the impulses of any particular cycle. During the first part of the cycle the station selecting relays (such as relay S0 at each field station are selected in accordance with the positions of the code jumpers which are effective for that cycle of operations. At each field station a different combination of code jumper connections is provided so that each station requires the reception of a distinctive code in order that this station may be selected and this code is determined in accordance with the positions of the corresponding group of code jumpers in the control oflice.

With the use of two separate code jumpers in the ofiice and at each station as illustrated, four different code combinations are possible, three of which may be employed for station selection with the fourth used for the phantom station code call. It is obvious that the code call for the station illustrated in Fig. 3 is because code jumpers 2 l6 and 222 at the station are connected for relay S0 to be maintained in its energized position in response to a and a impulse on the first and the second steps, respectively, which positions contact 2H of relay F to the right and to the left in response to these first two impulses.

The succeeding impulses will now be effective to govern the control relays of the selected station only. Upon the picking up of relay 3V in response to the third impulse, relay S0 is maintained energized throughout the remainder of the cycle at the station illustrated in Fig. 3 over a circuit extending from front contact 2l5 of relay S0 front contact 2|2 of relay 3V and winding of relay S0, to

Transmission of controls-Upon the reception .of the third impulse (following the third time space), relay SMR is energized for actuating its polar contact 224 to the right or to the left depending upon the character of the impulse. With lever SML in the control office in the position shown, a impulse is applied to the stepping line circuit which actuates the contacts of relay F to the right for closing an energizing circuit for relay SMR which extends from front contact 215 of relay S0 front contact 2l2 of relay 3V contact 2 of relay F in its right hand dotted position, front contact 2H3 of relay 3V and upper winding of relay SMR to This energization of relay SMR. positions its polar contact 224 to the right for applying energy to the normal operating winding of switch machine SM for operating the track switch to its normal locked position.

In the event that lever SML is in its left hand dotted position, then a impulse is applied to the stepping line for actuating the contacts of relay F to the left, thus closing a circuit for energizing relay SMR by way of its lower winding, which extends from front contact 2l5 of relay S0 front contact 2i2 of relay 3V contact 2 of relay F in its left hand dotted position, front contact 2!!! of relay 3V and lower winding of relay SMR to Since the connection to the lower winding of relay SMR is in opposition to the upper winding, contact 224 is actuated to its left hand dotted position for applying energy to the reverse operating winding of switch machine SM which operates the track switch to its reverse locked position.

In a similar manner additional steps may be provided for transmitting additional controls to the illustrated field station for governing the signals or such other controls as may be necessary.

End of control cycZe.Fo1lowing the application of the last impulse to the S line circuit, relay E is maintained energized for a period of time which is sufficiently long to allow relay SA to restore its contacts to their normal positions. This is due to relay E opening the stepping line circuit at back contact 32 for a comparatively long interval of time. Relay SA at the illustrated field station and other similar relays at other stations are likewise restored to their normal positions. Upon the opening of the front contacts of the SA relays in the control ofiice and in the field stations the stick circuits for the stepping relay banks are deenergized which allows these relays to restore to normal. It has previously been explained how the other relays in the control ofiice are deenergized at the end of the cycle. Relay S0 at the selected field station is deenergized because contact 2 of relay F is in its neutral position and front contact 2l2 of relay 3V is open.

Transmission of indications.Although this system is of the coded duplex type and indications may be transmitted from any station to the control office during the same cycle that controls are transmitted to the same or some other station, it is convenient to first explain the transmission of indications alone on a separate operating cycle before considering the duplex feature of the system.

There may be trains in various portions of the territory under the supervision of the operator and these trains may enter or leave track sections at two or more points in the territory at substantially the same time. Likewise the switches and signals at the various locations may be operated in such a way by the operator that several of these traflic controlling devices assume new conditions at substantially the same time. It will thus be evident that when two or more field stations have new indications to communicate to the control oflice at the same time, some means must be provided to permit only one of these stations to transmit at a time to avoid the transmission of false indications.

The manner in which field stations are allowed to transmit only one at a time in a predetermined order will be explained in connection with the the lockout feature, this feature being included in l the description following the description of the operation of the system with respectto the transmission of indications from a single field station; assuming that such station is the only :one having new indicationssito transmit at the beginning of the cycle. 1

Automatic start.,-Referring to Fig. 3, a change in the condition of the detector track section or a change inrcondition of other trainer controlling zdevicesat'the station may occur at any time, but

forconv'enience in'describing the operationof this portionof the system it will be assumed that relay T (or some other relay whichcontrols the transmission of indications) shifts its position to effect the deenergization of change relay CH The droppingof relay CH closes a circuit for picking up relay PLA which extends from back contacts 225rand 226 of relays SA and FP respectively, backcontact 221- ofrrelay CH back acontacts 228, 229 and 230 of relays W 2V and 3V respectivelyand winding of relay PLA to The-closingpf fronticontact 203 of relay PIA establishes aicircuit for energizing the A-B line which extends from the terminal of battery LBin the control OffiCG, back contact it of relay STR, winding ofirelay MB, B'line conductor l3,

resistance R back contact 205 of relay SA lower winding of relay L0 front contact 203 of zirelaypPLA ,-A- -line conductor l1, winding of relay MAand'back contact l5 ofzrelay'sTR tothe terminal'ofg'battery LB. Current flowing over this-circuit energizes relays MA and MB in the control oin'ceandin :responseto the energization of these two relays, relay ILC is picked up by meansrof a circuit not shown in detail in Fig l, butiwhichhas been shownrin Fig. 5 and extends through "back COIltEClTETU =of relayjSAand front contacts :60 and filsof relays MB and MA respectively to: the winding of relay iCH. With relay [CH once picked up it 'is' stuck up through a stick circuit including its stick contact 16' and back contact '15 of. relay LCS; Also with relay lCH energized ai pick-up circuit for relay iLC is closed=throughfront contact ll of relay ECH, this on the assumption that the system is at rest and-back contact .10 of. relay SA is closed and that: noneof thexrelays such'as relay SR are energized. i, The picking r-uprof: irelayrILC closes an energizing :circuit for relay'STR at front contact "l2. RelaySTR closes aspick-up circuit for relay NC which extends from.(+), backcontacts 39, 3B and 3l=of relays 3V, 2V and IV respectively, front ;contact- 34 of relayf-ILC, winding oi -relay NC and frontcontact "33 of' relay STR, to It will be noted that the switching of contacts M and E5 of relay-S'I'R: from their backto their front points deenergizesthe -A-Bline circuit and coninects these'two line conductors together.

In response to the picking up of relay NC the S line conductor is energized witha (conditioning) impulse, withthe return path for the current extending by way of the AB line conductors in multiple. This circuit extends from the terminalof battery LB,- back contact I2 of relay PC, front contact 16 of relay NC, front contacts H: "and M of: relay STR "through the windings =of :relays MA and MB, A and B line conductors I1 and I9 in multiple, front contact 203Jof relayPLA ,line (lower) winding of relay L0 back contact 205' of relay-SA resistance R back contact2fl4uof relay PLB over the B line conductor throughthe'other stations, to the end :stationhndthence by way of-rbackicontact 334 of .PC to the terminal of battery LB.

relay PLB atthe end station, winding of relay F winding of relay Fl, S line conductor l8,backcon-- tact 32 of relay E, winding of relay F, front contact iii of relay NC and'back contact 25 of relay It will be noted that the A line conductor extending to the other stations is open atthis time at back-contact 203 of relay PLA and at'front contact 2316 of relay In response to this impulse, relays F1, FP SA and similar relays at the other stations are picked up and when relay 'SA closes its front contact 266 and relay SA closes its front contact at the end station, the A and B line conductors (including all of the stations) are connectedin. multiple to the S line conductor.

In response to this first impulse, relay VP in the control office is picked up to close the previously described circuit for energizing relay E, which in turn marks the end of the conditioning on period by deenergizing the line circuits. The system now steps through a cycle asbefore except in this case relay NC is energized throughout the cycle because of front contacts 42, 43 and it being closed instead of contacts48, 52 and 53. This energization of relay NC causes the following impulses of the cycle to be negative in character.

The above described circuit for energizing the AB line conductors for initiating the system from the field station includes the line winding of relay LO which causes this relay to pick up and close a stick circuit for its local winding (after relay SA has picked up) extending from front contact 231 of relay SA front contact 232 and local winding of relay L0 to Relay L0 establishes the energizing circuit for relay FP at its front contact 202 so that stepping will be effective at this station during this cycle.

Relay L0 connects by way of its front contact 233 to bus 235 at this transmitting :field station, so that energy may be extended by way of the contacts of the relays which are to control indications, such as relays T M and the like, for energizing the PLA and PLB relays during this cycle in .a manner which will be later described. Since this is assumed to bev a cycle for the transmission of indications alone, it will be understood that none of the SO relays will be picked up, because relay F (and similar relays at other stations) actuated its polar contact 2! l to the left which is ineffective to establish a pick up circuit for relay S0 Registration of a field station.-At the particular station having indications to transmit, lockout relay L0 is picked up and by virtue of its closed front contact 202 permits the operation of the stepping relay bank at this station in re sponse to the impulses in the S line circuit as repeated by relay FP It will be recalled that relay VP is picked up during the conditioning on period and stepping relays lV 2V and 3V are picked up during the first, second and third 01f periods respectively.

When relay FP closes its make-before-break front contact 226 the stick circuit of relay PLA is completed to at back contact 225 of relay SA After a comparatively long interval of time, relay 8A is picked up to open back contact 225 which de-energizes relay PLA It will be understood that the sequential operation of the MA and MB relays (if such operation takes place) during the conditioning on period .is

first stepping relay is not picked up until the time space following this on period.

When relay IV is picked up during the first off period, indication code transmitting relays PLA and PLB are conditioned in accordance with the particular indication code to be transmitted. This conditioning of the PLA and PLB relays is determined at this step in accordance with the positions of code jumpers 265 and 266 of Fig. 3.

For example, with code jumper 265 in its full line position no connection is established between the terminal of the battery (which is connected to bus 234) and the winding of relay PLA With code jumper 266 in its full line position a connection is established from on bus 234, code jumper 266, front contact 261 of relay IV back contacts 268 and 269 of relays 2V and 3V respectively and winding of relay PLB to This energization of relay PLB is maintained throughout the first on period so that inductance BL is inserted in the B line conductor because of open back contact 204.

Since relay PLA is de-energized, inductance AL in the A line conductor is short-circuited by a circuit extending from A line conductor I'I, back contact 203 of relay PLA and front contact 206 of relay SA to the opposite terminal of inductance AL This effects the comparatively quick energization of the A line conductor and the comparatively slow energization of the B line conductor at the beginning of the first on period which results in relay MA and relay F picking up their contacts before relay MB picks up its contacts.

With front contact 5I of relay MA closed before back contact 50 of relay MB is opened a circuit is established for picking up relay MBP. With relay MBP picked up during the first on period, it is stuck up until relay E picks up to mark the end of this on period over a circuit extending from back contact 55 of relay E, front contact 56 and winding of relay MBP, to Therefore relay MBP will be maintained in its energized position after relay M'B opens its back contact 50.

During this on period a circuit is established for energizing relay 2PT which positions its polar contacts to the right, which circuit extends from (B+) front contact I of relay MBP, front contact IOI of relay MB, back contacts I02 and I03 of relays 3V and 2V respectively, front contact I04 of relay IV and winding of relay 2PT, to (CN).

It will be obvious that the above illustrates one choice of the two indications transmitted during the first impulse period. The other choice of the two indications is transmitted when jumpers 265 and 266 are in their dotted line positions. In this event relay PLA is energized over a circuit extending from on bus 234, jumper 265, front contact 228 of relay IV back contacts 229 and 230 of relays 2V and 3V respectively and Winding of relay PLA to Since jumper 266 in its dotted line position is ineffective to complete the circuit to relay PLB the effect of this arrangement of the code jumpers is to quickly energize the B line conductor and to slowly energize the A line conductor. This causes relay MB to pick up before relay MA and to close a circuit for picking up relay MAP which extends from front contact 50 of relay MB, back contact 5| of relay MA and winding of relay MAP, to Relay MAP sticks itself over the circuit described in connection with the sticking of relay MBP.

In response to this code combination relay MAP energizes relay I PT in such a direction that its contacts are positioned to the right over a circuit extending from (3+), front contact I 05 of relay MAP, front contact I06 of relay MA, back contacts I01 and I08 of relays 3V and 2V respectively, front contact I09 of relay IV and winding of relay IPT, to (ON). In this instance relay MBP is not picked up so that (B) is connected to the winding of relay 2PT for positioning its polar contacts to their left hand dotted positions.

In the previously assumed case (jumpers 265 and 266 of Fig. 3 in their full line positions) relay I PT positions its polar contacts to the left because the above described circuit to the wind ing of relay IPT extends from (B) at back contact I 05 of relay MAP.

With the contacts of relay IPT positioned to the left and the contacts of relay 2PT positioned to the right, a circuit is closed for energizing station relay ST when the second step is taken and which extends from front contact I I0 of relay 2V, contact III of relay IPT in its left hand position, contact II2 of relay 2PT in its right hand position and winding of relay ST, to

In the above explanation it has been pointed out that relay IPT operates its polar contacts to the left in response to the quick building up of current in the A line conductor because relay MAP remains ole-energized due to the fact that relay MA picks up before relay MB. Also that relay IPT operates its polar contacts to the right in response to a slow building up of current in the A line conductor because relay MAP picks up due to relay MB picking up before relay MA.

It has also been pointed out that relay 2PT positions its polar contacts to the left in response to the quick building up of current in the B line conductor because relay MBP remains de-energized due to the fact that relay MB picks up before relay MA. Also that relay 2PT positions its polar contacts to the right in response to the slow building up of current in the B line conductor because relay MBP picks up due to the fact that relay MA picks up before relay MB.

From the above it will be observed that a first code combination is transmitted by causing the current to quickly build up in both the A and B line conductors so that relays MA and MB are picked up at approximately the, same time to prevent the picking up of either relay MAP or MBP, which results in relays IPT and 2PT positioning their polar contacts to the left.

A second code combination is transmitted by causing current to quickly build up in line A and slowly build up in line B for positioning the polar contacts of relay IPT to the left and the polar contacts of relay 2PT to the right.

A third combination is transmitted by causing current to slowly build up in line A and quickly build up in line B for positioning the polar contacts of relay IPT to the right and the polar contacts of relay 2PT to the left.

A fourth combination is transmitted by causing the current to slowly build up in both the A and B line conductors so that both relays MAP and MBP will be picked up over a circuit extending from front contact II3 of relay TC, back contact II 4 of relay F and back contacts 50 and 5| of relays MB and MA respectively to the windings of relays MBP and MAP respectively.

polar contacts of relays IPT and ZPT are Withboth relays MBP and MAP picked up the positioned to the right.

Relay TC is provided to enable the last mentioned combination to be used, this relay functioning to close its front contact H3 in a fixed period of time after relay PC closes its front contact 30"(or relay NC closes its front contact 3|) for energizing the S line circuit. This time is adjusted to be approximately the same as the time it takesrelay F to pick up with no limiting inductance in the return line circuit, comprising either line A or line B. This adjustment is made by adjusting inductance TL to permit relay TO to pick up in this fixed time. The result of this is that relay TC will pick up in response to the beginning of an on period in its usual time; but when limiting inductance is included in both the A and B line conductors, all three relays F, MA and MB will be comparatively slow in picking up. Therefore the above described circuit is completed for both relays MAP and MBP.

Transmission of indications-After thus having registered in the control office the particular field station which has indications to transmit, by picking up relay ST, for example, the remaining steps of the cycle are employed for the transmission of these indications from the registered station.

For example, with track relay T energized as indicated in Fig. 3, relay PLA is not picked up after the second step is taken so that the A line is quickly energized for quickly picking up relay MA. Since relay M is de-energized, relay PLB is picked up over a circuit including back contact 231 of relay M This inserts inductance BL into the B line circuit which causes the B. line conductor to be slowly energized so that relay MB will be picked up after relay MA is picked up for'completing a circuit for picking up relay MBP.

Since relay MAP is not picked up, (B) is connected through back contact I05, front contact I06 of relay MA, back contact .I'I of relay 3V, front contact I'08 of relay 2V, front contact II of relay ST and winding of relay IIR, to (CN). This positions the polar contact of relay IIR to the right which is effective to de-energize lamp OS as an indication that the track section is unoccupied.

With relay MBP picked up, (B+) is connected by way of front contacts I00 and ml of relays MBP and MB respectively, back contact I02 of relay 3V, front contact I03 of relay 2V and front contact I16 of relay ST to the winding of relay 21R. This positions the polar contact of relay 21R to the left. 1

Relay T will be de-energized when the associated track section is occupied for picking up relay PLA whichresults in the A line conductor being slowly energized for picking up relay MAP as previously described. Relay MAP connects (B+) by way of its front contact I05 and over the previously described circuit to the winding of relay IIR for positioning the polar contact of this relay to its left hand dotted position which energizes lamp OS as an indication that the associated track section is occupied.

In the event that relay M is picked up when the second step is taken, then relay PLB is deenergized to quickly energize line conductor 13 for picking up relay MB to prevent the energization of relay MBP. Therefore (B) through back contact I00 of relay MBP is connected to the winding of relay 21R by way of front contact I03 of relay 2V and front contact I I6 of relay ST for positioning the polar contact of relay 21R to the right;

It will be understood that local circuits may be controlled by relay HR for indicating the condition of' the signals at the station as repeated by relayM 'It will likewise be evident that additional indication storing relays may be provided forselection on additional steps of the cycle for receiving additional indications from the registered station.

During a cycle of operations for the transmission of indications, relay CH at the transmitting station is restored to its picked up position by 'means of a circuit arrangement which is not shown so that it is in readiness to register any other change that may occur at that field station'.

' End of indication cycle-The step-by-step operations of the system and the impulsing of the S line circuit during an indication cycle are similar to those operations already explained in connection with a control cycle.- The S line circuit is opened for acomparatively long time interval after the last impulse is transmitted in a manner which has previously been explained in connection with a control cycle and which is effective to restore the system to normal. The dropping of relay ILC in the control office as a result of dropping of the relay SA de-energizes relay STR and disconnects the channel selecting circuits from relay NC at the front contacts of relay ILC.-

Lockout between field stations.--As previously mentioned it may happen that changes occur at a plurality of field stations at the same time or in rapid succession so that more than one field station will havenew indications to transmit at the beginning of a cycle. In order to prevent more than one station actively associating itself with the communication system during any particular cycle, lockout means are provided at each station which are effective to select that station nearest the control oflice having new indications to transmit at the beginning of a cycle.

Assuming that a change occurs at the field station illustrated in Fig. 3, which station is assumed to be the one nearest the control office, the de-energization of change relay CH closes its back contact 221 for effecting the energiza tion of relay PLA as previously described so that the normally de-energized AB line is energized to start a cycle ofoperations. It has previously been mntioned that relay L0 is picked up when the cycle is initiated from this field station, and that relays F FF and SA are picked up in response to the conditioning impulse. The closure of front contacts HI and 232 of relays SA and Lo respectively, complete the stick circuit for relay LO before the pick up circuit including the-line winding of relay L0 is opened at backcontact 205 of relay SA At other stations farther out the line, the picking up of the FP relays opens the pick up circuits of the associated PLA relays at back contacts similar to back contact 226 of relay FP so that the PLA relays at these other stations are prevented from picking up over circuits including back contacts similar to 22'Iof change relays at these other stations. Shortly after the picking up of the FP relays, the SA relays are picked up so that no other field station can pick up its PLA relayduring this cycle because of open back fee contacts on the SA relays similar to back contact 225 of relay SA In other words, the last chance that a change at a field station has for actively associating itself with the communication system ends when the FP relay at such a station is picked up. This means that the PLA relay (with suitable exponent) of a transmitting station must be energized for a sufficient period of time prior to the picking up of the contacts of the SA relay to allow the line winding of'the associated LO relay to be energized over the A B line circuit for picking up its contacts so that it may be stuck up after the picking up of the SA relay.

It will be assumed that relay CH at the first field station is de-energized and shortly after the closure of its back contact 221 the corresponding relay at the second station also becomes de-energized. Relay PLA at the first station is picked up and shortly thereafter the PLA relay at the second station is picked up. Upon the closure of front contact 2ll3of relay PLA at the first station the AB line circuit is energized to pick up relays MA and MB in the control ofiice for initiating the cycle in the manner previously described.

It will be recalled that the closure of front contacts 60 and BI of relays MB and MA respectively effects the energization of relay ILC for picking up relay STR to initiate the cycle. Relay NC is now energized so that a impulse is applied to the S line circuit, the return path being by way of the A andB line conductors in multiple. Since the line windings of the lockout relays are included in the A line conductor and since the A line conductor is open F FP and SA to pick up in sequence for completing the above described stick circuit for relay LO before its pick up circuit is de-energized.

The picking up of relay SA at the first station and the picking up of the SA relays at the other stations (including relay SA shown in the dotted rectangle in the upper right hand portion of Fig. 3) completes the continuity of the A line conductor.

At the second station which is assumed to have its CH relay dropped and its PLA relay picked up,,the F, FP and SA relays are also energized because the S line circuit through this station is complete. At the second station the picking up of the SA relay drops the associated PLA relay because of open back contact similar to 225 and since the line winding of the lockout relay at this station was not energized, the lockout relay remains down during this cycle. It will be understood that relay PLA at the first station is also'dropped when relay SA opens its back contact 225 so that relay PLA may be conditioned upon the succeeding steps of the cycle for conditioning the A line circuit to form this portion of the indication code. The dropping of relay PLA at the first station does not drop the associated lockout relay because of its previously described stick circuit.

In brief, the first field station recorded a change in condition prior to, or at the same time that a change was recorded at the second station, but the first field station is superior by reason of its geographic location. Irrespective of whether such changes occur sequentially as above assumed or whether they occur simultaneously, the station nearest the control ofiice will obtain energy through a front contact similar to 203 of relay PLA for energizing its lockout relay so that at the end of the conditioning period relay LO will be stuck up and remain up for the remainder of the cycle, while at the station farther out the line the lockout relay is not picked up and the PLA relay is dropped to remove the associated inductance from the A line circuit at this station.

Although the lookout feature has been explained with reference to the first station having preference over the second station it will be understood that similar conditions may exist between various combinations of stations in the system. It is believed, however, that the above explanation is sufficient for an understanding of all such combinations, remembering that in each case the station nearest the control ofiice which picks up its PLA relay before the picking up of the ET relays, has preference over other stations.

Two way transmission.1t has been pointed out that control and indication cycles may each occur separately or simultaneously. The operations for control and indication cycles alone have been described and it will now be pointed out how the system functions when controls and indications are transmitted during the same cycle. An actuation of the starting button in the control ofiice through the medium of relay SR results in the picking up of the CD relay during the time that the system is at rest and during any time up to the end of the period marked off by the picking up of relay SA in the control office. This circuit for relay CD is shown in Fig. 5 of the present disclosure and is also disclosed in the above mentioned application Ser. No. 711,383. In other words, if a field station has initiated the system which results in the picking up of relays ILC, STR, NC, F, FP and SA, all as described in connection with an indication cycle, the control office may pick up a CD relay during this period relay ILC cannot be picked up when the storing relay SR which is actuated in response to the operation of a starting button STB is in its energized position because energy is supplied to the winding of relay ILC through a back contact 13 of the storing relay (see Fig. 5).

Recalling that a field station can energize its lockout relay any time up to the picking up of its associated SA relay, it will be seen that a field station may be in condition to transmit its indications during the same cycle that the control ofiice transmits controls because relay CD can be picked up during the initiating period of a cycle initiated from a field station. In this connection it will be noted that when the field station initiates the cycle in advance of a control ofiice start, resulting in relay ILC being picked up and stuck up over a circuit including a front contact T0 of relay SA (see Fig. 5), then no CD relay can be picked up because their pick up circuits in- 7 5 clude this back contact 70 on relay SA as previously mentioned. This is necessary because when relay ILC is stuck up for a particular cycle it causes a phantom code comprising a series of impulses to be transmitted. With relay CD picked up and a field station having its lockout relay picked up atthe start of aparticular cycle, the first impulse of the cycle is determined as previously described. This impulse picks up all of the SO relays and determines that stepping at all stations will be started. The character of the impulses applied to theS line, as determined by the particular CD relay which is picked up, selects the required station by dropping out the SO relays at the stations not to be selected in the manner previously described. Since the lockout relay at a particular station is assumed to be picked up, stepping will continue at this station in the event that it is not the selected station for controls because of the closure of a front contact such as front contact 202 of the lookout relay.

The resulting cycle of operations is thus the same, insofar as the transmission of impulses over the S line for the selection of a station isconcerned, as was previously described in connection with a control cycle alone. Similarly the resulting operations of the cycle, insofar as the conditioning of the A and B line conductors is concerned, is the same asdescri bed for a cycle during which indications alone were transmitted. It is believed that the above brief explanation is sufficient to clearly indicate that, since the transmission of controlsand the transmission of indications are effected by the separate and distinct conditioning of the-line circuits, these transmissionsmay be combined and brought about during a single cycle of operations. Description ofmodification.'1he modification shown in abbreviated form in. Fig. 4 indicates a second method for detecting (in the control office) the time lag in the building up of current in the A and B'lines due to the inclusion of the inductance units such as AL and IBL. in these line conductors. In this modification the pilot relays (corresponding to relays IPT and ZPT of Fig. 2B) are neutral typerelays instead of the magnetic stick type. These relays are deenergized at the beginning of acycle when relay SA is picked up and their stick circuits are prepared when relay lV picks up.

These pilot relays IPT and 2PT are energized by the inductive impulses in the secondary windings of transformers, the primaries of which are included in the A and B line circuits. These sec- =ondary transformer windings include rectifiers in the circuits leading to the channelselecting arrangement through which the pilot relays are selected, so thatthese relays'may be picked up or not as determined by the indication trans mitted from the field station.

Local primary windings of the transformers are included in a local circuit in the control office connected across the stepping line and the A-B lines. This local circuit is designed to contain re sistance and inductance of values corresponding to theresistance and inductance of the line cir-- cults, so that when the inductance units such as AL andBL at a transmitting station are shortcircuited, current will build up in these local primary windings at the same rate (or at a slightly lesser rate) than in the primary windings includedin the line circuits.

When inductance unit AL for example, is ineluded-in lineA, current through the local primary winding of the transformer associated with this line builds up quicker than the current through the line primary winding of this transformer, thus producing a magnetic flux for causing an induced current to flow in the secondary winding of this transformer in series with the rectifier for energizing relay IPT. The rectifier is employed so that an exact balance between the line primary winding and the local winding of the transformer is not necessary, it being assumed that the surge of current produced in the secondary winding of this transformer will be of suflicient intensity and duration to energize a quick acting neutral type relay.

To describe the operation of the modification disclosed in Fig. 4 somewhat more in detail it will be assumed that the field station illustrated in Fig. 3 initiates the system into a cycle of operations by energizing the A-B line conductors for picking up relays MA and MB in the control office as previously described. In this connection it will be apparent that the MA and MB relays are for purpose of initiating the system from a transmitting field station and are not used for receiving indications. It will further be assumed that the field station illustrated in Fig. 3 transmits its indications in the manner previously described and it will be explained how the circuit modification of Fig. 4 functions to receive these indications.

With this explanation of the manner in which pilot relays IPT and 2PT are distinctively conditioned, it will be obvious how the indication receiving relays associated with the station which is registered in the oihce are likewise conditioned on the next step of the cycle as selected by the second stepping relay. It is therefore believed unnecessary to include the indication receiving relays in the Fig. 4 disclosure, since their operation may be understood from the pilot relay operation.

When relay E closes its back contact 32 to mark the beginning of the first on period, an energizing circuit is completed from one side of the line battery, back contact 32 of relay E, balancing resistance RS, local primary windings LPB and LPA of the transformers in series and front contact l5 of relay STR to the other side of the line battery. The constants of the circuit including these local primary windings and resistance RB are such that current builds up through these windings at the same (or at a slightly lesser) rate that current builds up in line primary windings PB and PA of these transformers when inductance units AL and BL of the transmitting station are short-circuited.

Since the transmission of this indication assumes relay PLB picked up (as previously described), inductance BL is included in the B line conductor but inductance AL is short-circuited out of the A line conductor. This means that current will build up through line primary winding PA and local primary winding LPA at approximately the same rate and since these windings are oppositely wound the effect on second ary winding SAT is neutralized so that no current is induced in this secondary winding. Therefore no current flows through rectifier RA to pilot relay lPT which results in this relay remaining deenergized.

Current builds up in the 13 line conductor at a slower rate than in the A lineconductor so that the current builds up through the line primary winding PB at a substantially lower rate than it builds up through the local primary winding LPB. Therefore these currents are not neutralized because the current through winding LPB reaches 

